Fluoroalkyl carboxylic acid derivative, method for producing fluorine-containing polymer, and aqueous dispersion of fluorine-containing polymer

ABSTRACT

This invention provides a novel compound which can be properly used as a surfactant, a method of producing a fluoropolymer, surfactant and a fluoropolymer aqueous dispersions using the novel compound. This invention is a fluoroalkylcarboxylic acid derivative which is represented by the general formula (i):
 
Rf 1 (OCH 2 CF 2 CF 2 ) n1 OCX 1 X 2 CF 2 (Rf 2 ) n2 COOM  (i)
 
wherein Rf 1  represents a straight or branched fluoroalkyl group containing 1 to 20 carbon atoms, which fluoroalkyl group may optionally contain 1 to 5 oxygen atoms in the principal chain thereof, Rf 2  represents a straight or branched fluoroalkylene group containing 1 to 25 carbon atoms, said fluoroalkylene group may optionally contain 1 to 5 oxygen atoms in the principal chain thereof, n1 represents an integer of 0 to 3, n2 represents an integer of 0 or 1, X 1  and X 2  are the same or different and each represents hydrogen atom or fluorine atom, and M represents NH 4  or a monovalent metal element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.10/562,730, which is a 371 of PCT Application No. PCT/JP2004/009445filed Jul. 2, 2004 and which claims benefit of JPA No. 2003-190250 filedJul. 2, 2003. The above-noted applications are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention relates to a fluoroalkylcarboxylic acidderivative, a surfactant, a method of producing fluoropolymers, and afluoropolymer aqueous dispersion.

BACKGROUND ART

So far disclosed as compounds obtainable by the ring opening reaction oftetrafluorooxetane are 2,2-difluoropropionic acid derivativesrepresented by XCH₂CF₂COY (wherein X is R¹O— or R²CH₂CF₂CF₂O— in whichR¹ and R² each is a saturated aliphatic group or halogenated saturatedaliphatic group containing 1 to 3 carbon atoms, for instance; and Y is—OR³ in which R³ is a saturated aliphatic group or halogenated saturatedaliphatic group containing 1 to 3 carbon atoms, for instance (cf. e.g.Patent Document 1).

However, no carboxylic acid salts are known as compounds obtainable bythe ring-opening reaction of tetrafluorooxetane. It is also unknownwhether tetrafluorooxetane-derived ring-opening reaction products can beused as surfactants.

Partially fluorinated compounds represented by Rf—(CH₂)_(m)—Rf′—COOM (inwhich m is 1 to 3, Rf is a perfluoroalkyl or perfluoroalkoxy groupcontaining 3 to 8 carbon atoms, Rf′ is a straight or branchedperfluoroalkylene group containing 1 to 4 carbon atoms and M is NH₄, Li,Na, K or H) are known as surfactants useful in polymerizing fluorinatedmonomers (cf. e.g. Patent Document 2). In this document, however, thereis no description or suggestion about the extents of the reduction insurface tension as brought about by such surfactants or the mean primaryparticle sizes of the polymers obtained by using the surfactants.

-   -   Patent Document 1: Japanese Kokai Publication H02-223538 (Claim        1)    -   Patent Document 2: Japanese Kokai Publication H10-212261

DISCLOSURE OF INVENTION

Problems which the Invention is to Solve

In view of the above-discussed state of the art, it is an object of thepresent invention to provide a novel compound which can be properly usedas a surfactant, a method of producing a fluoropolymer, a surfactant anda fluoropolymer aqueous dispersion using the novel compound.

Means for Solving the Problems

The present invention provides a fluoroalkylcarboxylic acid derivativewhich is represented by the general formula (i):Rf¹(OCH₂CF₂CF₂)_(n1)OCX¹X²CF₂(Rf²)_(n2)COOM  (i)wherein Rf¹ represents a straight or branched fluoroalkyl groupcontaining 1 to 20 carbon atoms, which fluoroalkyl group may optionallycontain 1 to 5 oxygen atoms in the principal chain thereof, Rf²represents a straight or branched fluoroalkylene group containing 1 to25 carbon atoms, said fluoroalkylene group may optionally contain 1 to 5oxygen atoms in the principal chain thereof, n1 represents an integer of0 to 3, n2 represents an integer of 0 or 1, X¹ and X² are the same ordifferent and each represents hydrogen atom or fluorine atom, and Mrepresents NH₄ or a monovalent metal element.

The invention provides a fluoroalkylcarboxylic acid derivative which isrepresented by the general formula (ii):Rf¹(OCH₂CF₂CF₂)_(n1)OCHX¹CF₂(Rf²)_(n2)COOM  (ii)wherein Rf¹ represents a straight or branched fluoroalkyl groupcontaining 1 to 20 carbon atoms, said fluoroalkyl group may optionallycontain 1 to 5 oxygen atoms in the principal chain thereof, Rf²represents a straight or branched fluoroalkylene group containing 1 to25 carbon atoms, said fluoroalkylene group may optionally contain 1 to 5oxygen atoms in the principal chain thereof, n1 represents an integer of0 to 3, n2 represents an integer of 0 or 1, X¹ represents hydrogen atomor fluorine atom, and M represents NH₄ or a monovalent metal element.

The invention also provides a surfactant which comprises thefluoroalkylcarboxylic acid derivative.

The invention further provides a method of producing a fluoropolymer,wherein the above fluoroalkylcarboxylic acid derivative is used as asurfactant in carrying out a polymerization in an aqueous medium.

The invention further provides a fluoropolymer aqueous dispersion,wherein a particle comprising a fluoropolymer is dispersed in an aqueousmedium in the presence of the above fluoroalkylcarboxylic acidderivative or the surfactant of the invention.

The invention further provides a fluoropolymer powder which is obtainedby coagulating the above fluoropolymer aqueous dispersion.

The invention further provides a fluoropolymer aggregate obtained bycoagulating the above fluoropolymer aqueous dispersion, which is apolytetrafluoroethylene powder, a powder or a pellet each comprising amelt-processible resin, or a coagulation comprising an elastomericpolymer.

The invention further provides a film/membrane which is obtained bycoating, impregnation or cast film formation using the abovefluoropolymer aqueous dispersion.

The invention further provides a molded article which is obtained bymolding using the above fluoropolymer powder or the above fluoropolymeraggregate.

The invention still further provides a method of producing afluoroalkylcarboxylic acid derivative, which comprises producing theabove fluoroalkylcarboxylic acid derivative by converting afluorocarboxylic acid fluoride represented by the general formula (3):Rf¹(OCH₂CF₂CF₂)_(n1)OCX¹X²CF₂(Rf²)_(n2)COF  (3)wherein Rf¹, Rf², n1, n2, X¹ and X² are as defined hereinabove, to afluorocarboxylic acid salt.

In the following, the invention is described in detail.

One of the fluoroalkylcarboxylic acid derivatives of the invention is anovel compound represented by the general formula (i) given above.

The symbol Rf¹ in the above general formula (i) represents a straight orbranched fluoroalkyl group containing 1 to 20 carbon atoms. A preferredlower limit to the number of carbon atoms is 3, a more preferred lowerlimit is 1, a preferred upper limit is 15, a more preferred upper limitis 8, and a still more preferred upper limit is 6. The fluoroalkyl groupis a group resulting from substitution of one or more fluorine atoms fora part or the whole of the hydrogen atoms bound to the carbon atom(s) inthe corresponding alkyl group.

The fluoroalkyl group may optionally contain 1 to 5 oxygen atoms in theprincipal chain thereof. A preferred upper limit to the number of oxygenatoms in the group Rf¹ is 3. The number of oxygen atoms in Rf¹ ispreferably equal to zero.

Straight or branched fluoroalkyl groups containing 1 to 7 carbon atoms,which may optionally contain 1 to 3 oxygen atoms in the principal chainthereof, are preferred as Rf¹, and straight or branched perfluoroalkylgroups containing 1 to 7 carbon atoms, which contain no oxygen atom inthe principal chain thereof, are more preferred.

The oxygen atom or atoms which may be contained in the fluoroalkyl groupand/or fluoroalkylene group, when contained in the fluoroalkyl and/orfluoroalkylene group, form ether bonds.

Preferred as Rf¹ are CF₃—, CF₃CF₂—, CF₃CF₂CF₂—, (CF₃)₂CF—,CF₃CF₂CF₂CF₂—, CF₃CF₂CF₂OCF(CF₃) CF₂—, HCF₂CF₂CF₂—, and CF₃)₂CF(CF₃)CF₂—. More preferred as Rf¹ are CF₃CF₂CF₂—, (CF₃) ₂CF— andCF₃CF₂CF₂CF₂—. CF₃CF₂CF₂— is still more preferred as Rf¹.

In the above general formula (i), Rf² represents a straight or branchedfluoroalkylene group containing 1 to 25 carbon atoms. A preferred lowerlimit to the number of carbon atoms is 2, while a preferred upper limitis 20, a more preferred upper limit is 15, a still more preferred upperlimit is 12, and a most preferred upper limit is 7.

The above fluoroalkylene group may optionally contain 1 to 5 oxygenatoms in the principal chain thereof. A preferred upper limit to thenumber of oxygen atoms in Rf² is 4, and more preferred upper limit is 3.

Preferred as Rf² are —CF₂OCF₂—, —CF₂(OCF(CF₃)CF₂)_(n3)OCF(CF₃)— (inwhich n3 represents an integer of 0 to 4) and—CF₂(OCF(CF₃)CF₂)_(n4)(CF₂CF₂)_(n5)— (in which n4 represents an integerof 0 to 5 and n5 represents an integer of 0 to 6 provided that n4 and n5satisfy the relation 3×n4+2×n5≦20).

In the above general formula (i), n1 represents an integer of 0 to 3. Apreferred upper limit to n1 is 2, and a preferred lower limit is 1.

In the above general formula (i), n2 represents an integer of 0 or 1.Preferably, n2 is 0 (zero).

X¹ and X² in the above general formula (i) are the same or different andeach represents hydrogen atom or fluorine atom. Preferably, at least oneof X¹ and X² is fluorine atom.

M in the above general formula (i) represents NH₄ or a monovalent metalatom.

NH₄ is preferred as the above M in view of its being readily eliminableby heating treatment.

Another class of the fluoroalkylcarboxylic acid derivatives of theinvention comprises novel compounds represented by the general formula(ii) given above.

In the general formula (ii), Rf¹, Rf², n1, n2 and M are as definedabove.

In the general formula (ii), X¹ represents a hydrogen atom or a fluorineatom. The atom X¹ is preferably a fluorine atom.

As the fluoroalkylcarboxylic acid derivatives of the invention, theremay be mentioned, among others, the following:

-   Fluorocarboxylic acid salts containing an —OCH₂CF₂— group adjacent    to the salt-forming carboxyl group, such as    CF₃OCF(CF₃)CF₂OCH₂CF₂COONa, CF₃CF₂CF₂OCH₂CF₂COONa,    CF₃CF₂CF₂OCH₂CF₂CF₂OCH₂CF₂COONa, FCH₂CF₂CF₂OCH₂CF₂COONa,    CF₂HCF₂CF₂OCH₂CF₂COONa, CF₃CF₂CF₂CF₂OCH₂CF₂COONa,    CF₃OCF(CF₃)CF₂OCH₂CF₂COONH₄, CF₃CF₂CF₂OCH₂CF₂COONH₄,    CF₃CF₂CF₂OCH₂CF₂CF₂OCH₂CF₂COONH₄, FCH₂CF₂CF₂OCH₂CF₂COONH₄,    CF₂HCF₂CF₂OCH₂CF₂COONH₄ and CF₃CF₂CF₂CF₂OCH₂CF₂COONH₄;-   Fluorocarboxylic acid salts containing an —OCFHCF₂— group adjacent    to the salt-forming carboxyl group, such as    CF₃OCF(CF₃)CF₂OCFHCF₂COONa, CF₃CF₂CF₂OCFHCF₂COONa,    CF₃CF₂CF₂OCH₂CF₂CF₂OCFHCF₂COONa, FCH₂CF₂CF₂OCFHCF₂COONa,    CF₂HCF₂CF₂OCFHCF₂COONa, CF₃CF₂CF₂CF₂OCFHCF₂COONa,    CF₃OCF(CF₃)CF₂OCFHCF₂COONH₄, CF₃CF₂CF₂OCH₂CF₂CF₂OCFHCF₂COONH₄,    FCH₂CF₂CF₂OCFHCF₂COONH₄, CF₃CF₂CF₂OCFHCF₂COONH₄,    CF₂HCF₂CF₂OCFHCF₂COONH₄ and CF₃CF₂CF₂CF₂OCFHCF₂COONH₄; and-   Fluorocarboxylic acid salts containing an —OCFHCF₂— group adjacent    to the salt-forming carboxyl group, such as    CF₃OCF(CF₃)CF₂OCF₂CF₂COONa, CF₃CF₂CF₂OCF₂CF₂COONa,    CF₃CF₂CF₂OCH₂CF₂CF₂OCF₂CF₂COONa, FCH₂CF₂CF₂OCF₂CF₂COONa,    CF₂HCF₂CF₂OCF₂CF₂COONa, CF₃CF₂CF₂CF₂OCF₂CF₂COONa,    CF₃OCF(CF₃)CF₂OCF₂CF₂COONH₄, CF₃CF₂CF₂OCF₂CF₂COONH₄,    CF₃CF₂CF₂OCH₂CF₂CF₂OCF₂CF₂COONH₄, FCH₂CF₂CF₂OCF₂CF₂COONH₄,    CF₂HCF₂CF₂OCF₂CF₂COONH₄ and CF₃CF₂CF₂CF₂OCF₂CF₂COONH₄.

The fluoroalkylcarboxylic acid derivatives of the invention arecharacterized in that they contain —O—CX¹X²CF₂— adjacent toRf¹(OCH₂CF₂CF₂)_(n1)— (Rf¹, X¹, X² and n1 being as defined above) asindicated by the general formula (i) given above. The group —O—CX¹X²CF₂—can be introduced by ring-opening addition of tetrafluorooxetane by themethod of producing fluoroalkylcarboxylic acid derivatives according tothe invention, which is to be described later herein.

The method of producing a fluoroalkylcarboxylic acid derivativeaccording to the invention comprises producing the abovefluoroalkylcarboxylic acid derivative by converting a fluorocarboxylicacid fluoride represented by the general formula (3):Rf¹(OCH₂CF₂CF₂)_(n1)OCX¹X²CF₂(Rf²)_(n2)COF  (3)wherein Rf¹, Rf², n1, n2, X¹and X² are as defined above, to afluorocarboxylic acid salt.

In the method of producing the fluoroalkylcarboxylic acid derivativeaccording to the invention, the above group Rf¹ is preferably a straightor branched fluoroalkyl group containing 5 to 7 carbon atoms and, inthis case, the fluoroalkyl group may optionally contain 1 to 5 oxygenatoms in the principal chain thereof.

The conversion of the fluorocarboxylic acid fluoride represented by thegeneral formula (3) given above to the fluorocarboxylic acid salt ispreferably carried out by

-   (A) a method comprising converting the terminal —COF group in the    general formula (3) to —COOH by hydrolysis using an acid and    converting the —COOH to —COOM by neutralization with an alkali,-   (B) a method comprising esterifying the terminal —COF group in the    general formula (3) and, after separation of the ester, converting    the ester moiety to —COOM by saponification, or-   (C) a method comprising esterifying the terminal —COF group in the    general formula (3) and, after separation of the ester, converting    the ester moiety to —COOM by saponification, then converting the    latter to —COOH using an acid and then converting this to —COOM by    neutralization with an alkali.

When n2 in the general formula (3) is 1, the fluorocarboxylic acidfluoride represented by the general formula (3) is preferably a productobtained by reacting an intermediate fluorocarboxylic acid fluoriderepresented by the general formula (2):Rf¹(OCH₂CF₂CF₂)_(n1)OCHX¹X²CF₂COF  (2)wherein Rf¹, n1, X¹ and X² are as defined above, withtetrafluoroethylene and iodine in an aprotic polar solvent to therebyconvert the terminal —COF in the above general formula (2) to—CF₂OCF₂CF₂I, followed by further conversion of the latter to—CF₂OCF₂COF by reaction with oleum, or a product obtained by convertingthe terminal —COF in the general formula (2) to—CF₂(OCF(CF₃)CF₂)_(p)OCF(CF₃)COF [p being an integer of 0 to 5] byaddition of hexafluoropropylene oxide, converting the terminal—CF(CF₃)COF to —CF(CF₃)I via —CF(CF₃)COI and converting —CF(CF₃)I to—CF(CF₃)(CF₂CF₂)_(q)I (q being an integer of 1 to 5), followed byfurther conversion to —CF(CF₃)(CF₂CF₂)_(q-1)CF₂COF.

When n2 in the general formula (3) is 0, the fluorocarboxylic acidfluoride represented by the general formula (3) is the intermediatefluorocarboxylic acid fluoride represented by the general formula (2)itself. Therefore, the above-mentioned reaction for addition of Rf² isnot indispensable. However, the method of producing thefluoroalkylcarboxylic acid derivative according to the inventionincludes the method of converting the intermediate fluorocarboxylic acidfluoride to the fluorocarboxylic acid salt as well.

The intermediate fluorocarboxylic acid fluoride represented by thegeneral formula (2) is preferably a second intermediate represented bythe general formula (2a):Rf¹(OCH₂CF₂CF₂)_(n1)OCHFCF₂COF  (2a)wherein Rf¹ and n1 are as defined above, as obtained by monofluorinatinga first intermediate represented by the general formula (1):Rf¹(OCH₂CF₂CF₂)_(n1)OCH²CF₂COF  (1)wherein Rf¹ and n1 are as defined above, or a third intermediaterepresented by the general formula (2b):Rf¹(OCH₂CF₂CF₂)_(n1)OCF₂CF₂COF  (2b)wherein Rf¹ and n1 are as defined above, as obtained by difluorinatingthe above first intermediate.

While the intermediate fluorocarboxylic acid fluoride represented by thegeneral formula (2) is preferably the second intermediate or thirdintermediate, as mentioned above, they may also be the firstintermediate itself.

The first intermediate is obtained by the ring-opening addition reactioninvolving ring-opening addition of tetrafluorooxetane to afluorine-containing acid fluoride represented by Rf³COF (in which Rf³ isa group derived from the Rf¹ group by elimination of one carbon atom).The ring-opening addition reaction will be described later herein.

The method of producing the fluoroalkylcarboxylic acid derivativeaccording to the invention is not particularly restricted but may be,for example, the method comprising

-   (1) the step of synthesizing the first intermediate    Rf¹(OCH₂CF₂CF₂)_(n1)OCH₂CF₂COF (Rf¹ and n1 being as defined above)    by ring-opening addition of tetrafluorooxetane to a    fluorine-containing fluoride represented by Rf³COF (in which Rf³ is    a group derived from the Rf¹ group by elimination of one carbon    atom) and, if necessary, fluorinating the first intermediate to    thereby convert the same to the second intermediate represented by    the general formula (2a) or the third intermediate represented by    the general formula (2b), and-   (2) the step of converting the terminal —COF in the above-mentioned    first, second or third intermediate to —(Rf²)_(n2)COOM.

In the above step (1), the fluorine-containing fluoride represented byRf³COF, when Rf¹ is, for example, CF₂CF₂CF₂—, is CF₃CF₂COF.

The above step (1) can be carried out, for example, according to themethod (described in Patent Document 1) comprising reacting thefluorine-containing acid fluoride represented by Rf³COF withtetrafluorooxetane in an aprotic polar solvent using the fluoride ion asa catalyst to give Rf¹OCH₂CF₂COF.

As the ion source for the fluoride ion, there may be mentioned alkalimetal fluorides such as cesium fluoride, potassium fluoride and sodiumfluoride, and tetramethylurea, among others.

As the aprotic polar solvent, there may be mentioned glymes such astetraglyme, diglyme, triglyme and polyglymes, THF, dioxane, DMF, DMA,HMPT and acetonitrile, among others.

The reaction between the fluorine-containing acid fluoride andtetrafluorooxetane can be carried out generally at a temperature of −50to 200° C. and a pressure of 0 to 1 MPa for 1 to 24 hours with stirring.

The progress of the reaction between the fluorine-containing acidfluoride and tetrafluorooxetane is monitored by gas chromatography, forinstance.

As for the catalyst addition level on the mole basis, the catalyst ispreferably used in an amount of 1 to 100 mole percent relative to thetotal amount of the fluorine-containing acid fluoride used. A morepreferred lower limit is 5 mole percent, and a more preferred upperlimit is 50 mole percent.

The amount of the solvent is not particularly restricted but the solventmay be used in a fairly large amount in cases where the pressurepredicted from the boiling point of the fluorine-containing acidfluoride employed and the reaction temperature should be lowered.However, an excessively large amount makes it difficult to separate andrecover the product after the reaction and, therefore, the catalyst ispreferably used in an amount of 0.1 to 1000 times the volume of thefluorine-containing acid fluoride used. A more preferred lower limit ishalf, and a more preferred upper limit is 2 times.

The proportion of the fluorine-containing acid fluoride relative to thetotal number of moles of the fluorine-containing acid fluoride andtetrafluorooxetane is preferably within the range of 9 to 95 molepercent. From the yield viewpoint, a more preferred lower limit to theproportion of the fluorine-containing acid fluoride may be set at 15mole percent and a more preferred upper limit to 50 mole percent. Whenn1 in the above general formula (i) or (ii) is 0 (zero), a still morepreferred lower limit is 45 mole percent and a still more preferredupper limit is 55 mole percent. When n1 in the above general formula (i)or (ii) is 1, a still more preferred lower limit is 30 mole percent anda still more preferred upper limit is 40 mole percent. When n1 in theabove general formula (i) or (ii) is 3, a still more preferred lowerlimit is 20 mole percent and a still more preferred upper limit is 30mole percent.

The reaction vessel to be used for the reaction between thefluorine-containing acid fluoride and tetrafluorooxetane is notparticularly restricted provided that it is securely airtight and allowsstirring. It may be a metal-made vessel, a plastic vessel made of afluororesin or a like plastic, or a glass vessel (although possiblysusceptible to erosion in case of intrusion of water). The reactionvessel should be selected taking the reactant quantity, reactiontemperature and reaction pressure into consideration.

The reaction between the fluorine-containing acid fluoride andtetrafluorooxetane may allow addition of two or more molecules oftetrafluorooxetane to each fluorine-containing acid fluoride molecule,and the reaction product generally becomes a mixture of firstintermediate molecules differing in the number of tetrafluorooxetanemolecules added. Therefore, a procedure for separating the firstintermediate with a specific addition level or level range (hereinaftersometimes referred to as “desired first intermediate”) from among thefirst intermediate mixture mentioned above is preferably carried outprior to fluorination.

The above separation procedure can be carried out by means ofrectification using a rectification column having an appropriate numberof plates. The appropriate number of plates is determined by the boilingrange of the fluorine-containing acid fluoride fraction to be excluded,the boiling point of the aprotic polar solvent, and the boiling point ofthe desired first intermediate, among others.

After separation of the desired first intermediate by the aboveseparation procedure, the desired first intermediate can be subjected tofluorination according to need.

The fluorination can be carried out using any of the conventionalfluoride radical generating sources such as CoF₃, AgF₂, UF₆, OF₂, N₂F₂,OF₃OF, IF₅, ClF₃ and like fluorinating reagents; and gaseous F₂.

In the above fluorination, a metal vessel or a fluororesin vessel, forinstance, is used.

In carrying out the fluorination, the use of a solvent is not requiredbut a solvent may be used. When a polar solvent such as acetonitrile,for instance, is used, the second intermediate can be obtained with ahigh yield. Complete fluorination gives the above third intermediate.

When the second intermediate and third intermediate are obtained in amixture form, they can be separated from each other by aseparation/purification method utilizing the difference in boilingpoint, for example by rectification or distillation. Since thedifference in boiling point between the second intermediate and thirdintermediate is small, a rectification column with a high number ofplates is required for obtaining high-purity products.

In cases where it is difficult to separate the desired firstintermediate by the above separation procedure, the terminal —COR isesterified using an alcohol such as methanol, and the desired firstintermediate-derived esterification product is separated from theconversion product, namely a mixture of first intermediate-derivedesterification products represented by the general formula (4):Rf¹(OCH₂CF₂CF₂)_(n1)OCH₂CF₂COOR⁴  (4)wherein Rf¹ and n1 are as defined above and R⁴ represents an alkyl groupcontaining 1 to 10 carbon atoms which may optionally contain one or morefluorine atoms as substituent(s) for one or more hydrogen atoms.

The first intermediate-derived terminal esterification product mentionedabove is the product of conversion of the terminal to —COOR⁴ (R⁴ beingas define above) with the number of tetrafluorooxetane molecules addedbeing the same in the desired first intermediate.

The separation of the desired first intermediate-derived terminalesterification product can be generally realized by aseparation/purification method utilizing the difference in boilingpoint, for example rectification or distillation. Since the firstintermediate-derived terminal esterification product is higher inboiling point as compared with the first intermediate, the separationmay become easy in some instances depending on the aprotic polar solventused in combination.

Unlike the case of the terminal being —COF, there is no fear of theterminal esterification product reacting with moisture to generatehydrogen fluoride and thus cause erosion of glass. Therefore, aglass-made apparatus can be used with safety.

In the step (1) mentioned above, the first intermediate is anintermediate for the production of fluoroalkylcarboxylic acidderivatives of the general formula (i) in which each of X¹ and X² ishydrogen atom. The second intermediate is an intermediate for theproduction of fluoroalkylcarboxylic acid derivatives of the generalformula (i) in which either one of X¹ and X² is fluorine atom. The thirdintermediate is an intermediate for the production offluoroalkylcarboxylic acids of the general formula (i) in which each ofX¹ and X² is fluorine atom. The term “intermediate” so referred tohereinafter without addition of “first”, “second” or “third” includes,within the meaning thereof, the above-mentioned first intermediate,second intermediate and third intermediate.

When n2 is 0 (zero) in the general formula (3), the above-mentioned step(2) consists in converting the terminal —COF in the intermediate to—COOM (M being as defined above).

The intermediate, when hydrolyzed with an acid and, after elimination ofthe byproduct hydrogen fluoride, subjected to distillation, gives ahigh-purity fluoroalkylcarboxylic acid represented by the generalformula (5):Rf¹(OCH₂CF₂CF₂)_(n1)OCX¹X²CF₂COOH  (5)wherein Rf¹, n1, X¹ and X² are as defined above, which can then beconverted to the fluoroalkylcarboxylic acid derivative of the inventionby neutralization with an alkali. This method is the above-mentionedmethod (A) of the invention itself comprising converting afluorocarboxylic acid fluoride to the fluorocarboxylic acid salt.

The first intermediate terminal esterification product can be convertedto the fluoroalkylcarboxylic acid derivative of the invention by themethod comprising saponifying the terminal —COOR⁴ (R⁴ being as definedabove) to —COOM (M being as defined above) (this method corresponds tothe above-mentioned method (B) comprising converting a fluorocarboxylicacid fluoride to the fluorocarboxylic acid salt), or by the methodcomprising saponifying —COOR⁴(R⁴ being as defined above), thenconverting the resulting group to —COOH using an acid and converting—COOH to —COOM by neutralization with an alkali (this method correspondsto the above-mentioned method (C) comprising converting afluorocarboxylic acid fluoride to the fluorocarboxylic acid salt).

When n2 in the above general formula (3) is 1, the above step (2) can becarried out, for example, by:

-   Method (a): the method comprising reacting the intermediate with    tetrafluoroethylene and iodine in acetonitrile to convert the    terminal —COF of the intermediate to —CF₂OCF₂CF₂I (as described    in J. F. C. 10 (1977) 85 to 110), converting the latter to    —CF₂OCF₂COF by reaction with oleum, then hydrolyzing the terminal    —COF in —CF₂OCF₂COF, and neutralizing the resulting acid;-   Method (b): the method comprising carrying out the reaction for    converting the terminal —COF of the intermediate to    —CF₂(OCF(CF₃)CF₂)_(p)OCF(CF₃)COF (p being an integer of 0 to 5) by    addition of hexafluoropropylene oxide (as described in Japanese    Kokai Publication S57-54147), the reaction for converting the    terminal —CF(CF₃)COF in the above terminal    —CF₂(OCF(CF₃)CF₂)_(p)OCF(CF₃) COF to —CF(CF₃) COI and then    converting the latter to —CF(CF₃)I (as described in Japanese Kokai    Publication H05-9150) and the reaction for converting the above    terminal —CF(CF₃)I to —CF(CF₃)(CF₂CF₂)_(q)I (q being an integer of 1    to 5) and then converting the latter to —CF(CF₃)(CF₂CF₂)_(q-1)CF₂COF    (as described in Japanese Kokai S58-152839), in that order and then    hydrolyzing the terminal —COF in the above    —CF(CF₃)(CF₂CF₂)_(q-1)CF₂COF, followed by neutralization.

In the above-mentioned method (a) and method (b), the hydrolysis may becarried out by the method using an acid such as dilute sulfuric acid,and the neutralization may be carried out by the method using an alkalimetal hydroxide such as sodium hydroxide, or aqueous ammonia.

The fluoroalkylcarboxylic acid derivatives of the invention, which havethe structure mentioned above, show good properties as surfactants andcan be adequately used, for example, as surfactants in the production offluoropolymers by polymerization and also as dispersants in preparingfluoropolymer aqueous dispersions.

The fluoroalkylcarboxylic acid derivatives of the invention reduce thesurface tension to a lesser extent as compared with the conventionalsurfactants. The reduction in surface tension means an increase inemulsifying power and, therefore, compounds less capable of reducing thesurface tension are generally unsuited for use as emulsifiers inpolymerization processes. However, the fluoroalkylcarboxylic acidderivatives of the invention, in spite of their low surface tensionreducing ability, show a high level of emulsifying power and, when usedas emulsifiers in the production of fluoropolymer by polymerization,which will be described later herein, can increase the average primaryparticle diameter of fluoropolymer particles.

The average primary particle diameter is the mean value of diameters offluoropolymer particles in a dispersion in a state such that thefluoropolymer after completion of the polymerization reaction has notyet been subjected to any procedure that substantially alters theconcentration thereof.

The fluoroalkylcarboxylic acid derivatives of the inventionsatisfactorily produce the effect mentioned above even when used singly.However, two or more species may be used simultaneously. Further, thefluoroalkylcarboxylic acid derivatives of the invention may be used incombination with one or more of the known compounds having surfaceactivity.

The term “fluoropolymer” as used herein means a polymer containingcarbon atom-bound fluorine atoms. In accordance with the invention, thefluoropolymer is obtained by polymerizing one or morefluorine-containing monomer species and may be one obtained bycopolymerization of a fluorine-free monomer as well. The“fluorine-containing monomer” is a monomer containing at least onefluorine atom bound to a carbon atom. The fluoropolymer will bedescribed later herein.

The fluoroalkylcarboxylic acid derivatives of the invention can beproperly used in or as photographic emulsions, photographic processingagents, cosmetics, detergents, foaming agents, antifoaming agents,greases, lubricants, metal surface finishing agents, mold releaseagents, abrasive agents, waxes, crystal growth controlling agents,cement additives, digesting agents, etching agents, leather treatmentagents, pharmaceuticals, pesticides, insecticides, lumping inhibitors,repellents, and ordinary surfactants for polymerization or dispersants.In the above respective fields of application, the fluoroalkylcarboxylicacid derivatives of the invention may be used singly or two or more ofthem may be used simultaneously, or they may be used in admixture withone or more other substances. In the above respective fields ofapplication, those methods which are known in the art can be employed.

The surfactants of the invention comprise at least one of thefluoroalkylcarboxylic acid derivatives of the invention.

The surfactants of the invention, even when they comprise only one ofthe fluoroalkylcarboxylic acid derivatives of the invention, cansatisfactorily function as surfactants. However, they may comprise twoor more of the fluoroalkylcarboxylic acid derivatives of the invention.

The surfactants of the invention may further contain one or more othercompounds having surface activity in addition to at least one of thefluoroalkylcarboxylic acid derivatives.

The other compounds having surface activity are not particularlyrestricted but may be, for example, anionic, cationic, nonionic orbetaine-type surfactants. These surfactants may be hydrocarbon-derivesones.

The surfactants of the invention may further contain at least oneadditive in addition to at least one of the fluoroalkylcarboxylic acidderivatives of the invention and the optional other compound(s) havingsurface activity. The additive is not particularly restricted but may beone generally used in ordinary surfactants, for example a stabilizer.

The surfactants of the invention can be suitably used as emulsifiers tobe present in polymerization processes for the production offluoropolymers and, in addition, can be suitably used also asdispersants for dispersing the fluoropolymers obtained by polymerizationin an aqueous medium.

The method of producing fluoropolymers according to the invention usesat least one of the above-mentioned fluoroalkylcarboxylic acidderivatives as a surfactant in carrying out the polymerization in anaqueous medium.

While the use of only one of the fluoroalkylcarboxylic acid derivativescan produce the surfactant effect in the process of producingfluoropolymers, two or more species may be used simultaneously. Thefluoroalkylcarboxylic acid derivatives may be used in combination withone or more other compounds having surface activity.

In producing fluoropolymers in accordance with the invention, thepolymerization is carried out by charging a polymerization vessel withan aqueous medium, at least one of the fluoroalkylcarboxylic acidderivatives, and a monomer or monomers, if necessary together with oneor more additives, stirring the contents in the reaction vessel,maintaining the reaction vessel at a predetermined polymerizationtemperature, and then adding a predetermined amount of a polymerizationinitiator to initiate the polymerization reaction. After the start ofthe polymerization reaction, a monomer or monomers, a polymerizationinitiator, a chain transfer agent and/or at least one of thefluoroalkylcarboxylic acid derivatives of the invention may beadditionally fed to the reaction vessel in accordance with the intendedpurpose.

In the above polymerization, the polymerization temperature is generally5 to 120° C., and the reaction pressure is generally 0.05 to 10 MPa. Thepolymerization temperature and polymerization pressure are to beproperly selected according to the monomer species used, the desiredpolymer molecular weight and the rate of reaction.

The “aqueous medium” so referred to hereinabove is a reaction medium inwhich the polymerization is to be carried out and means awater-containing liquid. The aqueous medium is not particularlyrestricted provided that it contains water. It may be composed of waterand a fluorine-free organic solvent, such as an alcohol, ether orketone, and/or a fluorine-containing organic solvent having a boilingpoint not higher than 40° C. It may be water containing one of theorganic solvents mentioned above. In carrying out suspensionpolymerization, for instance, water and a fluorine-containing organicsolvent may be used in combination.

The above-mentioned aqueous medium can be used as the aqueous medium inthe fluoropolymer aqueous dispersions of the invention, which will bedescribed later herein.

In the above-mentioned polymerization, the fluoroalkylcarboxylic acidderivatives are preferably used at a total addition level of 0.0001 to20% by mass relative to the aqueous medium. A more preferred lower limitis 0.001% by mass, a more preferred upper limit is 15% by mass, a stillmore preferred upper limit is 10% by mass, and a most preferred upperlimit is 1% by mass. The addition level is to be properly determinedtaking into consideration the monomer species used and the desiredpolymer molecular weight, among others.

In the above polymerization, the fluoroalkylcarboxylic acid derivativesare more preferably added at the time of starting the polymerization ata total addition level of 0.0001 to 20% by mass relative to the aqueousmedium.

The polymerization initiator is not particularly restricted but may beany of those capable of radical generation within the polymerizationtemperature range mentioned above. This, the oil-soluble and/orwater-soluble polymerization initiators known in the art can be used.Further, the polymerization can also be initiated by using a reducingagent, for instance, in combination to form a redox system. Theconcentration of the polymerization initiator is to be properly selectedaccording to the monomer species, the desired polymer molecular weightand the rate of reaction.

Further, in the above polymerization, the rate of polymerization and themolecular weight can be adjusted by adding one or more of the chaintransfer agents and radical scavengers known in the art in accordancewith the intended purpose.

The fluoropolymers are the products of polymerization of one or morefluorine-containing monomers and, according to the intended purpose, oneor more fluorine-free monomers may also be copolymerized.

As the fluorine-containing monomers, there may be mentioned, amongothers, fluoroolefins, preferably fluoroolefins containing 2 to 10carbon atoms; fluorinated cyclic monomers; and fluorinated alkyl vinylethers represented by the formula —CY₂═CYOR⁵ or —CY₂═CYOR⁶OR⁵ (in whichY is H or F, R⁵ is an alkyl group containing 1 to 8 carbon atoms with apart or the whole of the hydrogen atoms having been substituted by afluorine atom or atoms and R⁶ is an alkylene group containing 1 to 8carbon atoms with a part or the whole of the hydrogen atoms having beensubstituted by a fluorine atom or atoms).

The fluoroolefins preferably contain 2 to 6 carbon atoms. As thefluoroolefins containing 2 to 6 carbon atoms, there may be mentioned,for example, tetrafluoroethylene [TFE], hexafluoropropylene [HFP],chlorotrifluoroethylene [CTFE], vinyl fluoride, vinylidene fluoride[VDF], trifluoroethylene, hexafluoroisobutylene andperfluorobutylethylene. As preferred examples of the fluorinated cyclicmonomers, there may be mentioned perfluoro-2,2-dimethyl-1,3-dioxole[PDD] and perfluoro-2-methylene-4-methyl-1,3-dioxolane [PMD].

The group R⁵ in the above-mentioned fluorinated alkyl vinyl etherspreferably contains 1 to 4 carbon atoms and, more preferably, one inwhich all the hydrogen atoms have been replaced by fluorine. The groupR⁶ preferably contains 2 to 4 carbon atoms and, more preferably, is onein which all the hydrogen atoms have been replaced by fluorine atoms.

As the fluorine-free monomers mentioned above, there may be mentionedhydrocarbon-based monomers reactive with the fluorine-containingmonomers mentioned above. The hydrocarbon-based monomers include, amongothers, alkenes such as ethylene, propylene, butylenes and isobutylene;alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butylvinyl ether, isobutyl vinyl ether and cyclohexyl vinyl ether; vinylesters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinylisobutyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinylcaprylate, vinyl caprate, vinyl versatate, vinyl laurate, vinylmyristate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinylp-tert-butylbenzoate, vinyl cyclohexanecarboxylate, vinylmonochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate,vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate,vinyl hydroxyacetate, vinyl hydroxypropionate, vinyl hydroxybutyrate,vinyl hydroxyvalerate, vinyl hydroxyisobutyrate and vinylhydroxycyclohexanecarboxylate; alkyl allyl ethers such as ethyl allylether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether andcyclohexyl allyl ether; and alkyl allyl esters such as allyl acetate,allyl propionate, allyl butyrate, allyl isobutyrate and allylcyclohexanecarboxylate.

The fluorine-free monomers further include functional group-containinghydrocarbon-based monomers. As the functional group-containinghydrocarbon-based monomers, there may be mentioned, for example,hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether,hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutylvinyl ether and hydroxycyclohexyl vinyl ether; carboxylgroup-containing, fluorine-free monomers such as itaconic acid, succinicacid, succinic anhydride, fumaric acid, fumaric anhydride, crotonicacid, maleic acid, maleic anhydride and perfluorobutenoic acid; glycidylgroup-containing, fluorine-free monomers such as glycidyl vinyl etherand glycidyl allyl ether; amino group-containing, fluorine-free monomerssuch as aminoalkyl vinyl ethers and aminoalkyl allyl ethers; amidegroup-containing, fluorine-free monomers such as (meth)acrylamide andmethylolacrylamide.

As the fluoropolymers suitably producible by the production method ofthe invention, there may be mentioned TFE polymers in which the monomeraccounting for the highest monomer mole fraction in the polymer(hereinafter “most abundant monomer”) is TFE, VDF polymers in which themost abundant monomer is VDF, and CTFE polymers in which the mostabundant monomer is CTFE.

The TFE polymers may suitably be TFE homopolymers, or copolymers derivedfrom (1) TFE, (2) one or more fluorine-containing monomers other thanTFE, which contain 2 to 8 carbon atoms, in particular HFP and/or CTFE,and (3) another monomer or other monomers. As the other monomersmentioned above under (3), there may be mentioned, for example,fluoro(alkyl vinyl ether) species having an alkyl group containing 1 to5 carbon atoms, in particular 1 to 3 carbon atoms; fluorodioxole;perfluoroalkylethylenes; ω-hydroperfluoroolefins, etc.

The TFE polymers may also be copolymers of TFE and one or morefluorine-free monomers. The fluorine-free monomers are, for example,alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers.The TFE polymer may further be copolymers of TFE, one or morefluorine-containing monomers containing 2 to 8 carbon atoms and one ormore fluorine-free monomers.

Suitable examples of the VDF polymers are, among others, VDFhomopolymers [PVDF], and copolymers composed of (1) VDF and (2) one ormore fluoroolefins other than VDF, which contain 2 to 8 carbon atoms, inparticular TFE, HFP and/or CTFE, and (3) perfluoro(alkyl vinyl ether)species having an alkyl group containing 1 to 5 carbon atoms, inparticular 1 to 3 carbon atoms.

The CTFE polymers may suitably be CTFE homopolymers, or copolymerscomposed of (1) CTFE, (2) one or more fluoroolefins other than CTFE,which contain 2 to 8 carbon atoms, and (3) one or more perfluoro(alkylvinyl ether) species having an alkyl group containing 1 to 5 carbonatoms, in particular 1 to 3 carbon atoms.

The CTFE polymers may further be copolymers of CTFE and one or morefluorine-free monomers and, as the fluorine-free monomers, there may bementioned alkenes such as ethylene and propylene; vinyl esters; andvinyl ethers, among others.

The fluoropolymers produced by the production method of the inventionmay be glass-like, plastic or elastomeric. These are noncrystalline orpartially crystalline and can be subjected to compression bakingprocessing, melt processing or non-melt processing.

In accordance with the production method of the invention, there cansuitably be produced, for example, (I) polytetrafluoroethylene polymers[PTFE polymers] as non-melt processible resins, (II) ethylene/TFEcopolymers [ETFE], TFE/HFP copolymers [FEP] and TFE/perfluoro(alkylvinyl ether) copolymers [PFA, MFA, etc.] as melt-processible resins, and(III) such elastomeric copolymers as TFE/propylene copolymers,TFE/propylene/third monomer copolymers (the third monomer being VDF,HFP, CTFE, perfluoro(alkyl vinyl ether) and/or the like),TFE/perfluoro(alkyl vinyl ether) copolymers; HFP/ethylene copolymers,HFP/ethylene/TFE copolymers; PVDF; VDF/HFP copolymers, HFP/ethylenecopolymers, VDF/TFE/HFP copolymers and like thermoplastic elastomers;and fluorine-containing segmented polymers described in Japanese PatentPublication S61-49327.

The perfluoro(alkyl vinyl ether) referred to above is represented by theformula:Rf⁴(OCFQ¹CF₂)_(j)(OCR⁷Q²CF₂CF₂)_(k)(OCF₂)_(h)OCF═CF₂wherein Rf⁴ represents a perfluoroalkyl group containing 1 to 6 carbonatoms, j, k and h are the same or different and each represents aninteger of 0 to 5, Q¹, Q² and R⁷ are the same or different and eachrepresents F or CF₃.

The above-mentioned non-melt processible resins (I), melt-processibleresins (II) and elastomeric polymers (III), which are suitablyproducible by the production method of the invention are preferablyproduced in the following manner.

(I) Non-melt Processible Resins

In carrying out the production method of the invention, thepolymerization for producing PTFE polymers is generally carried out at apolymerization temperature of 10 to 100° C. and a polymerizationpressure of 0.05 to 5 MPa.

In the above polymerization, a pressure-resistant reaction vesselequipped with a stirrer is charged with pure water and thefluoroalkylcarboxylic acid derivative of the invention and, afterdeoxygenation, further charged with TFE, the temperature is raised to apredetermined level, and a polymerization initiator is added to initiatethe reaction. Since otherwise the pressure lowers with the progress ofthe reaction, an additional quantity of TFE is fed to the reactionvessel continuously or intermittently so as to maintain the initialpressure. After completion of feeding of a predetermined amount of TFE,the feeding is stopped, the TFE remaining in the reaction vessel ispurged, and the temperature is returned to room temperature. Thereaction is thus finished.

In producing the PTFE polymers mentioned above, one or more of variousmodifier monomers known in the art can be used in combination. Thepolytetrafluoroethylene polymers [PTFE polymers] so referred to hereinconceptually include not only TFE homopolymers but also those copolymersof TFE and a modifier monomer or monomers which are non-melt processible[hereinafter sometimes referred to as “modified PTFEs”]).

As the modifier monomers, there may be mentioned, among others,perhaloolefins such as HFP and CTFE; fluoro(alkyl vinyl ether) specieshaving an alkyl group containing 1 to 5, in particular 1 to 3, carbonatoms; fluorinated cyclic monomers such as fluorodioxole;perhaloalkylethylenes; and ω-hydroperhaloolefins. The modifier monomerfeeding may be carried out initially all at once, or continuously, orintermittently in portions, according to the intended purpose and thefeeding of TFE.

The modifier monomer content in the modified PTFEs is generally withinthe range of 0.001 to 2 mole percent.

In producing the PTFE polymers, the above-mentionedfluoroalkylcarboxylic acid derivates can be used within the range ofusage in the method of producing fluoropolymers according to theinvention. Generally, they are used at an addition level of 0.0001 to 5%by mass relative to the aqueous medium. The fluoroalkylcarboxylic acidderivative concentration is not particularly restricted provided that itis within the above range but the addition is generally carried out atthe time of start of the polymerization at a level not higher than thecritical micelle concentration (CMC). When the addition level isexcessively high, acicular particles with a large aspect ratio areformed, hence the aqueous dispersion becomes gel-like and the stabilityis impaired.

In producing the PTFE polymers, persulfate salts (e.g. ammoniumpersulfate) or organic peroxides such as disuccinoyl peroxide anddiglutaroyl peroxide may be used as the polymerization initiator, eithersingly or in the form of a mixture of these. These may also be used incombination with a reducing agent such as sodium sulfite to give redoxsystems. Further, during polymerization, the radical concentration inthe system can be adjusted by adding a radical scavenger such ashydroquinone or catechol or a peroxide-decomposing agent such asammonium sulfite.

In producing the PTFE polymers, use can be made of any of the knownchain transfer agents, for example saturated hydrocarbons such asmethane, ethane, propane and butane, halogenated hydrocarbons such aschloromethane, dichloromethane and difluoromethane, alcohols such asmethanol and ethanol, and hydrogen. Those which are gaseous at ordinarytemperature and ordinary pressure are preferred.

The chain transfer agent is generally used in an amount of 1 to 1000ppm, preferably 1 to 500 ppm, relative to the total feed of TFE.

In producing the PTFE polymers, use can further be made, as a dispersionstabilizer for the reaction system, of 2 to 10 parts by mass, per 100parts by mass of the aqueous medium, of a saturated hydrocarbon whichcontains not less than 12 carbon atoms, is substantially inert to thereaction and occurs as a liquid under the reaction conditions mentionedabove. Furthermore, ammonium carbonate, ammonium phosphate or the likemay be added as a buffering agent for adjusting the pH during reaction.

At the time of completion of the polymerization, the PTFE polymerconcentration, on the solid matter basis, in the aqueous dispersion is10 to 40% by mass, with an average primary particle diameter of 0.05 to5000 μm. By the use of the fluoroalkylcarboxylic acid derivative of theinvention, in particular, aqueous dispersions containing PTFE polymerparticles with a very small particle diameter not exceeding 0.2 μm canbe obtained. The PTFE polymers at the time of completion of thepolymerization have a number average molecular weight of 1,000 to10,000,000.

The aqueous PTFE polymer dispersion is subjected to coagulation anddrying steps to give a fine powder, which can be used in various fieldsof application.

In subjecting the aqueous PTFE polymer dispersion to coagulation, theaqueous dispersion obtained by emulsion polymerization, for example apolymer latex, is generally diluted to a polymer concentration of 10 to20% by mass using water and, after pH adjustment to a neutral oralkaline level under certain circumstances, stirred, in a vesselequipped with a stirrer, more vigorously than the stirring duringreaction. The coagulation may also be carried out by stirring whileadding, as a coagulating agent, a water-soluble organic compound such asmethanol or acetone, an inorganic salt such as potassium nitrate orammonium carbonate or an inorganic acid such as hydrochloric acid,sulfuric acid or nitric acid or the like. The coagulation may also becarried out continuously using an in-line mixer or the like.

When one or more of pigments for coloration and/or of various fillersfor improvements in mechanical properties are added prior to coagulationor during coagulation, pigmented or filled PTFE polymer fine powdergrades can be obtained with the pigment(s) and/or filler(s) uniformlydispersed therein.

The drying of the wet powder obtained by coagulation of the aqueous PTFEpolymer dispersion is generally effected using such means as vacuum,high-frequency or hot air while maintaining the wet powder in acondition such that it flows little, preferably it stands still.Friction among powder particles at elevated temperatures, in particular,generally exerts unfavorable influences on the PTFE polymer in finepowder form. This is because this kind of the particles comprising PTFEpolymer have a property such that they readily fibrillate upon exposureto even a weak shearing force and lose their original stable particlestructure.

The above drying is carried out at a drying temperature of 10 to 250°C., preferably 100 to 200° C. The PTFE polymer fine powder thus obtainedis preferably used for molding and, as proper uses thereof, there may bementioned, among others, tubes for use in hydraulic or fuel systems inairplanes or automobiles, and, further, flexible hoses for transportingliquid chemicals, steam or the like, and electric wire coatings orcoverings.

The aqueous PTFE polymer dispersion obtained by the above-mentionedpolymerization, when supplemented with a nonionic surfactant, isstabilized and, after further concentration, is preferably used invarious fields of application in the form of a composition supplementedwith an organic or inorganic filler(s) according to the intendedpurpose. The above composition, when applied to metal or ceramicsubstrates, can give coated surfaces having nonstickiness and a lowcoefficient of friction and excellent in gloss, wear resistance, weatherresistance and heat resistance. Thus, it is suited for use in coatingrolls and cooking utensils and impregnating processing of glass cloths.

(II) Melt-processible Resins

-   (1) In the production method of the invention, the polymerization    for producing FEP is preferably carried out generally at a    polymerization temperature of 60 to 100° C. and a polymerization    pressure of 0.7 to 4.5 MPa.

The monomer composition (on the % by mass basis) of the FEPs ispreferably TFE:HFP=(60 to 95):(5 to 40), more preferably (85 to 90):(10to 15). The FEPs may be ones modified with a perfluoro(alkyl vinylether) as a third component used in a proportion within the range of 0.5to 2% by mass relative to the sum of the monomers.

In the polymerization of the FEPs, the fluoroalkylcarboxylic acidderivatives mentioned above can be used within the usage range for theproduction method of the invention. Generally, they are used at anaddition level of 0.0001 to 5% by mass relative to the aqueous medium.

In the polymerization of the FEPs, use is preferably made, as a chaintransfer agent, of cyclohexane, methanol, ethanol, carbon tetrachloride,chloroform, methylene chloride or methyl chloride, for instance, and, asa pH buffering agent, of ammonium carbonate, disodium hydrogen phosphateor the like.

-   (2) In the production method of the invention, the polymerization    for producing TFE/perfluoro(alkyl vinyl ether) copolymers, such as    PFA and MFA copolymers, is preferably carried out generally at a    polymerization temperature of 60 to 100° C. and a polymerization    pressure of 0.7 to 2.5 MPaG.

Preferred as the monomer composition (in mole percent) for theTFE/perfluoro(alkyl vinyl ether) copolymers is TFE:(perfluoro alkylvinyl ether)=(95 to 99.7):(0.3 to 5), more preferably (98 to 99.5):(0.5to 2). Preferably used as the perfluoro(alkyl vinyl ether) are thoserepresented by the formula: CF₂═CFORf (in which Rf is a perfluoroalkylgroup containing 1 to 6 carbon atoms).

In the polymerization of the TFE/perfluoro(alkyl vinyl ether)derivatives, the fluoroalkylcarboxylic acid derivatives mentioned abovecan be used within the usage range for the production method of theinvention. Generally, however, they are used at an addition level of0.0001 to 2% by mass relative to the aqueous medium.

In the polymerization of the TFE/perfluoro(alkyl vinyl ether)copolymers, use is preferably made, as a chain transfer agent, ofcyclohexane, methanol, ethanol, carbon tetrachloride, chloroform,methylene chloride, methyl chloride, methane or ethane, for instance,and, as a pH buffering agent, of ammonium carbonate, disodium hydrogenphosphate or the like.

-   (3) In the production method of the invention, the polymerization    for producing the ETFE copolymers is preferably carried out    generally at a polymerization temperature of 20 to 100° C. and a    polymerization pressure of 0.5 to 0.8 MPaG.

Preferred as the monomer composition (in mole percent) of the ETFEs isTFE:ethylene=(50 to 99):(50 to 1). The ETFEs may be those modified witha third monomer in a proportion within the range of 0 to 20% by massrelative to the sum of the monomers. The ratio is preferablyTFE:ethylene:third monomer=(70 to 98):(30 to 2):(4 to 10). Preferred asthe third monomer are 2,3,3,4,4,5,5-heptafluoro-2-pentene(CH₂═CFCF₂CF₂CF₂H) and 2-trifluoromethyl-3,3,3-trifluoropropene((CF₃)₂C═CH₂).

In the polymerization of the ETFEs, the fluoroalkylcarboxylic acidderivatives mentioned above can be used within the usage range for theproduction method of the invention. Generally, they are used at anaddition level of 0.0001 to 2% by mass relative to the aqueous medium.

In the polymerization of the ETFEs, use is preferably made, as a chaintransfer agent, of cyclohexane, methanol, ethanol, carbon tetrachloride,chloroform, methylene chloride, methyl chloride or the like.

(III) Elastomeric Polymers

In carrying out the polymerization for producing elastomeric polymersaccording to the method of the invention, a pressure-resistant reactionvessel equipped with a stirrer is charged with pure water and thefluoroalkylcarboxylic acid derivative of the invention and, afterdeoxygenation, further charged with the monomers, the temperature israised to a predetermined level, and a polymerization initiator is addedto initiate the reaction. Since otherwise the pressure lowers with theprogress of the reaction, additional quantities of the monomers are fedto the reaction vessel continuously or intermittently so as to maintainthe initial pressure. After completion of feeding of predeterminedamounts of the monomers, the feeding is stopped, the monomers remainingin the reaction vessel are purged away, and the temperature is returnedto room temperature. The reaction is thus finished. In the case ofemulsion polymerization, the polymer latex formed is preferably takenout of the reaction vessel continuously.

In particular when thermoplastic elastomers are to be produced, it isalso possible to employ the method of accelerating the eventual rate ofpolymerization as compared with the conventional polymerizations bysynthesizing fine polymer particles once at a high surfactantconcentration and, after dilution, further carrying out thepolymerization, as disclosed in International Publication WO 00/01741.

In producing the elastomeric polymers, the reaction conditions are to beproperly selected from the viewpoint of the desired physical propertiesof the polymer and of the polymerization rate control. Generally, thepolymerization is carried out at a polymerization temperature of −20 to200° C., preferably 5 to 150° C., and a polymerization pressure of 0.5to 10 MPaG, preferably 1 to 7 MPaG. Preferably, the pH of thepolymerization medium is maintained generally at 2.5 to 9 with a pHadjusting agent, which is to be described later herein, in theconventional manner, for instance.

As the monomers to be used in producing the elastomeric polymers, theremay be mentioned vinylidene fluoride as well as fluorine-containing,ethylenically unsaturated monomers containing at least the same numberof fluorine atoms as the number of carbon atoms and capable ofcopolymerizing with vinylidene fluoride.

As the fluorine-containing ethylenically unsaturated monomers, there maybe mentioned, among others, trifluoropropene, pentafluoropropene,hexafluorobutene and octafluorobutene. Among them, hexafluoropropene isparticularly suited for use in view of the characteristics of theelastomers obtainable when it blocks the polymer crystal growth. As thefluorine-containing, ethylenically unsaturated monomers, there mayfurther be mentioned trifluoroethylene, TFE, CTFE, etc., andfluorine-containing monomers having one or more chlorine and/or brominesubstituents may also be used. Perfluoro(alkyl vinyl ether) species, forexample perfluoro(methyl vinyl ether), can also be used. TFE and HFP arepreferred for the production of the elastomeric polymers.

Preferred as the monomer composition (in % by mass) of the elastomericpolymers is vinylidene fluoride:HFP:TFE=(20 to 70):(20 to 60):(0 to 40).Elastomeric polymers having this composition show good elastomercharacteristics, chemical resistance and heat stability.

In the polymerization of the elastomeric polymers, thefluoroalkylcarboxylic acid derivatives mentioned above can be usedwithin the usage range for the production method of the invention.Generally, they are used at an addition level of 0.0001 to 5% by massrelative to the aqueous medium.

In the polymerization of the elastomeric polymers, any of the inorganicradical polymerization initiators known in the art can be used as thepolymerization initiator. Those water-soluble inorganic peroxides knownin the art, for example sodium, potassium and ammonium persulfate,perphosphate, perborate, percarbonate and permanganate, are particularlyuseful as the inorganic radical polymerization initiator. The radicalpolymerization initiator can be further activated by a reducing agentsuch as sodium, potassium or ammonium sulfite, bisulfite, metabisulfite,hyposulfite, thiosulfate, phosphite or hypophosphite, or by a readilyoxidizable metal compound such as a ferrous salt, cuprous salt or silversalt. Ammonium persulfate is a suitable inorganic radical polymerizationinitiator, and the combined use of ammonium persulfate and sodiumbisulfite in a redox system is more preferred.

The level of addition of the polymerization initiator is properlyselected within the range of 0.0001 to 10% by mass, preferably 0.01 to5% by mass, relative to the sum of the monomers, depending on thedesired molecular weight of the polymer and the polymerization reactionrate.

In the polymerization of the above elastomeric polymers, any of thechain transfer agents known in the art can be used. In the case of PVDFpolymerization, hydrocarbons, esters, ethers, alcohols, ketones,chlorine compounds and carbonates can be used and, in the case of thethermoplastic elastomers, hydrocarbons, esters, ethers, alcohols,chlorine compounds and iodine compounds can be used. Among them, acetoneand isopropyl alcohol are preferred in the case of PVDF polymerizationand, in the case of thermoplastic elastomer polymerization, isopentane,diethyl malonate and ethyl acetate are preferred from the viewpoint thatthe rate of reaction is hardly lowered thereby, and I(CF₂)₄I, I(CF₂)₆I,ICH₂I and like diiodide compounds are preferred from the viewpoint thatthe polymer termini can be iodinated and the polymer can be used as areactive one.

The usage of the chain transfer agent is generally 0.5×10⁻³ to 5×10⁻³mole percent, preferably 1.0×10⁻³ to 3.5×10⁻³ mole percent, relative tothe total amount of the monomers fed.

In the polymerization of the elastomeric polymers, the polymerization ofPVDF can be preferably carried out using a paraffin wax or the like asan emulsion stabilizer, and the polymerization of the thermoplasticelastomers can be preferably carried out using a phosphate salt, sodiumhydroxide, potassium hydroxide or the like as a pH adjusting agent.

At the time of completion of the polymerization, the elastomericpolymers produced in accordance with the invention have a solid matterconcentration of 10 to 40% by mass, an average primary particle diameterof 0.03 to 1 μm, preferably 0.05 to 0.5 μm, and a number averagemolecular weight of 1,000 to 2,000,000.

The average primary elastomeric polymer particle diameter can bedetermined, for example, by using a dynamic light scattering measuringdevice equipped with a He—Ne, Ar or like laser light source.

The elastomeric polymers obtained by the invention can be converted,according to need, to dispersions suited for rubber molding processingby adding a dispersion stabilizer such as a hydrocarbon-derivedsurfactant, and concentrating, for instance. The dispersions are treatedby pH adjustment, coagulation, heating, etc. The respective treatmentsare carried out in the following manner.

The pH adjustment consisting in adjusting the pH to 2 or below by addinga mineral acid such as nitric acid, sulfuric acid, hydrochloric acid orphosphoric acid and/or a carboxylic acid containing not more than 5carbon atoms and having a pK=4.2 or below, for instance.

The coagulation is carried out by adding an alkaline earth metal salt.As the alkaline earth metal salt, there may be mentioned calcium ormagnesium nitrate, chlorate and acetate.

Either of the pH adjustment and the coagulation may be carried outfirst. Preferably, however, the pH adjustment is carried out first.

After both procedures, the elastomers are washed with an equal volume ofwater to remove the buffer solution, salt and other impurities occurringin slight amounts within the elastomers, followed by drying. The dryingis generally carried out in a drying oven at elevated temperatures ofabout 70 to 200° C. under circulating hot air.

The method of producing a fluoropolymer according to the inventiongenerally gives the fluoropolymer at a concentration of 5 to 70% by massbased on the aqueous dispersion obtained by the above polymerizationreaction.

A preferred lower limit to the fluoropolymer concentration in theaqueous dispersion is 10% by mass, a more preferred lower limit is 15%,a preferred upper limit is 40% by mass, a more preferred upper limit is35% by mass, and a still more preferred upper limit is 30% by mass.

The aqueous dispersions just after polymerization as obtained by theabove polymerization reaction may be concentrated or subjected todispersion stabilization treatment to give dispersions, or subjected tocoagulation or flocculation, followed by recovery and drying to givepowders, aggregates or other solid forms. The method of producingfluoropolymers according to the invention is to produce fluoropolymers,and the fluoropolymers produced may be the fluoropolymers dispersed inthe respective aqueous dispersions just after polymerization, or thefluoropolymers dispersed in the dispersions mentioned above, or thefluoropolymers in the form of the above-mentioned powders, aggregates orother solids.

The term “aqueous dispersion just after polymerization” means one notyet subjected to any procedure for substantially changing thefluoropolymer concentration after completion of the polymerizationreaction. Such procedure includes, among other, concentration,coagulation, flocculation, etc., and these procedures give rise to theformation of particles (secondary particles) increased in diameter as aresult of aggregation of fluoropolymer particles (primary particles) inthe aqueous dispersions just after polymerization.

The fluoropolymer aqueous dispersion of the invention is the dispersionwherein a particle comprising a fluoropolymer is dispersed in an aqueousmedium in the presence of the above-mentioned fluoroalkylcarboxylic acidderivative or the surfactant of the invention.

The fluoropolymer aqueous dispersion of the invention may be the aqueousdispersion just after polymerization, or the dispersion obtained bysubjecting the aqueous dispersion just after polymerization to suchprocedures as the above-mentioned concentration, dispersionstabilization treatment and so forth, or the dispersion resulting fromdispersing the powder of fluoropolymer in an aqueous medium in thepresence of the above-mentioned fluoroalkylcarboxylic acid derivative orthe surfactant of the invention.

In the fluoropolymer aqueous dispersion of the invention, the “aqueousmedium” is a dispersion medium, namely a water-containing liquid. Theaqueous dispersion medium is not particularly restricted provided thatit contains water and, thus, for example, any of the aqueous mediausable in the production method of the invention can be used. Theaqueous medium may be the aqueous medium itself used in thepolymerization.

In the fluoropolymer aqueous dispersion of the invention, theabove-mentioned fluoroalkylcarboxylic acid derivative of the inventionmay be in a state of ionic dissociation of the —COOM moiety in thegeneral formula (i) in the aqueous medium.

The fluoropolymer aqueous dispersion of the invention in which thefluoroalkylcarboxylic acid derivative of the invention has a goodbalance between the affinity for the fluoropolymer and the affinity forthe aqueous medium can exhibit an excellent dispersing force just as inthe case of the use thereof as a surfactant in the production methodmentioned above.

The fluoropolymer aqueous dispersion of the invention, when it is anaqueous dispersion just after polymerization, preferably has a numberaverage primary particle diameter of about 0.03 to 1 μm. Thefluoropolymer aqueous dispersion of the invention, even when it has anumber average primary particle diameter within the above range, isexcellent in dispersion stability and mechanical stability and, forexample, can be prevented from adhering to the polymerization vesselinside wall or stirrer blade in the step of polymerization. A morepreferred lower limit is 0.05 μm, and a more preferred upper limit is0.5 μm.

The primary particle concentration is preferably about 5 to 70% by mass.A more preferred lower limit to that concentration is 10% by mass, astill more preferred lower limit is 15% by mass, and a preferred upperlimit is 60% by mass.

On the other hand, the above fluoropolymer aqueous dispersion, when itis a dispersion obtained by concentration and dispersion stabilizationtreatment, among others, contains secondary particles of thefluoropolymer preferably at a concentration of 30 to 70% by mass.

In the fluoropolymer aqueous dispersion of the invention, theconcentration of the fluoroalkylcarboxylic acid derivative is preferably0.0001 to 20% by mass. At levels lower than 0.0001% by mass, thedispersion stability may be poor and, at levels exceeding 20% by mass,the dispersing effect is no more proportional to the abundance thereofand this is of no practical use. A more preferred lower limit to theabove content is 0.001% by mass, a more preferred upper limit to theabove content is a concentration of 10% by mass and a more preferredupper limit is 2% by mass.

The fluoropolymer aqueous dispersion of the invention may be oneprepared as a dispersion by subjecting the aqueous dispersion just afterpolymerization to such procedures as concentration and dispersionstabilization treatment.

The concentration can be carried out by any of those methods known inthe art, and the dispersion can be concentrated to a fluoropolymerconcentration of 40 to 70% by mass according to the intended use of thedispersion. The concentration procedure may impair the dispersionstability in certain instances. In such cases, a dispersion stabilizermay further be added.

As the dispersion stabilizer, any of the above-mentionedfluoroalkylcarboxylic acid derivatives or other various surfactants maybe added. The various dispersion stabilizers include, but are notlimited to, nonionic surfactants such as polyoxyalkylene alkyl ethers,in particular polyoxyethylene ethers such as polyoxyethylene alkylphenylethers (e.g. Triton X-100 (trademark) of Rohm and Haas), polyoxyethyleneisotridecyl ether (Dispanol TOC (trademark) of NOF (Nippon Oil and Fat)Corp.) and polyoxyethylenepropyl tridecyl ether.

The total content of the dispersion stabilizers is preferably 0.5 to 20%by mass relative to the solid matter in the dispersion. At levels lowerthan 0.5% by mass, the dispersion stability may be poor and, at levelsexceeding 20% by mass, the dispersing effect is no more proportional tothe abundance thereof and this is of no practical use. A more preferredlower limit to the above total content is 2% by mass and a morepreferred upper limit is 12% by mass.

In some fields of application, the aqueous dispersion obtained bycarrying out the polymerization can also be subjected to dispersionstabilization treatment without concentration to give a fluoropolymeraqueous dispersion having a long pot life. As the dispersion stabilizerto be used, there may be mentioned the same ones as described above.

The uses of the fluoropolymer aqueous dispersion are not particularlyrestricted but, when it is applied as the aqueous dispersion as it is,the following uses may be mentioned among others: coating of substrateswhich comprises applying it to the substrates and drying the coatings,if necessary followed by baking; impregnation of nonwoven fabrics, resinmoldings and other porous supports which comprises impregnating thesupports with the dispersion, followed by drying, if necessary furtherfollowed by baking; and cast film formation which comprises applying thedispersion onto substrates such as glass substrates, drying the coatedsubstrates and, if necessary after immersion in water, peeling off thecoatings from the substrates to give thin films or membranes. In theseapplications, the dispersion is used as an aqueous dispersion typecoating composition, an electrode binder, or a water repellentcomposition for electrodes, for instance.

The fluoropolymer aqueous dispersion of the invention can be used as anaqueous coating composition after incorporation of one or more knownformulating ingredients selected from among pigments, thickening agents,dispersing agents, antifoaming agents, antifreezing agents, film-formingauxiliaries and the like and/or further compounding of another polymericcompound.

The fluoropolymer film/membrane obtained by coating, impregnation orcast film formation using the above-mentioned fluoropolymer aqueousdispersion also constitutes an aspect of the present invention.

As other uses of the fluoropolymer aqueous dispersion of the invention,there may be mentioned those uses in which a powder obtained bysubjecting the fluoropolymer aqueous dispersion to coagulation orflocculation to recover the polymer and drying the same, if desiredfollowed by granulation is utilized.

The coagulation or flocculation can be carried out employing any of themethods known in the art. For example, the method comprising adding acoagulant (or flocculant) to the aqueous dispersion with stirring tocause coagulation (or flocculation), the method comprising freezing andthawing the aqueous dispersion to cause coagulation (freeze coagulationmethod), the method comprising only mechanically stirring the aqueousdispersion at a high speed to cause coagulation (mechanical coagulationmethod), or the method comprising spouting the aqueous dispersion from anarrow nozzle and simultaneously causing water to evaporate (spraycoagulation method) is preferably employed. If necessary, a flocculationauxiliary may be added. The drying may be carried out by allowing thepolymer to stand at room temperature or may be carried out with heatingup to 250° C.

The fluoropolymer powder obtained by coagulating the above fluoropolymeraqueous dispersion also constitutes a further aspect of the invention.

The fluoropolymer aggregate obtained by coagulating the abovefluoropolymer aqueous dispersion, which is a fine powder comprising apolytetrafluoroethylene polymer powder, a powder or a pellet eachcomprising a melt-processible resin or a coagulation comprising anelastomeric polymer, also constitutes a further aspect of the presentinvention.

The powder obtained can be used, for example, as a molding materialsuited for paste extrusion molding, for instance, after incorporation ofa lubrication auxiliary, or as a powder coating composition, if desiredafter incorporation of a pigment or pigments.

The fluoropolymer molded article obtained by molding using the abovefluoropolymer powder or fluoropolymer aggregate also constitutes afurther aspect of the present invention.

EFFECTS OF THE INVENTION

The fluoroalkylcarboxylic acid derivative of the invention, which hasthe constitution described hereinabove, can be properly used as asurfactant in the production of fluoropolymers, as a dispersant forfluoropolymer aqueous dispersions and, further, in various other fieldsof application. The method of producing fluoropolymers according to theinvention, which uses the above-mentioned fluoroalkylcarboxylic acidderivative as a surfactant, can produce the fluoropolymers with greatefficiency.

Further, the fluoropolymer aqueous dispersion of the invention, in whicha particle comprising a fluoropolymer is dispersed in an aqueous mediumin the presence of the fluoroalkylcarboxylic acid derivative of theinvention or the surfactant of the invention, is excellent in stabilityand workability, among others.

BEST MODES FOR CARRYING OUT THE INVENTION

The following synthesis examples, working examples and comparativeexamples will illustrate the present invention. These synthesis examplesand working examples are, however, by no means limitative of the scopeof the invention.

The methods used for the measurements in the respective examples areshown below.

-   Solid matter concentration: Determined based on the weight loss    after 1 hour of drying of each aqueous dispersion at 150° C.-   Surface tension: Measured at 25° C. by the Wilhelmy method.-   Standard specific gravity (SSG): Measured according to ASTM D    1457-69.-   Average primary particle diameter (PTFE): Determined indirectly from    the transmittance of the incident light of 550 nm per unit length as    transmitted by each dispersion diluted to a solid matter    concentration of about 0.02% by mass based on a working curve    constructed by plotting such transmittance data against the average    particle diameter data obtained from electron photomicrographs.

The transmittance measurements were carried out using a Microtrac 9340UPA dynamic light scattering measuring apparatus (product of Honeywell).

-   Average primary particle diameter (elastomeric polymer): Determined    using a dynamic light scattering measuring apparatus equipped with a    He—Ne or Ar laser light source. Solid matter content (P.C.):    Determined from the weight loss after 1 hour of heating of 1 g of    each aqueous dispersion in a hot air oven at 150° C.-   Number average molecular weight: Measured by gel permeation    chromatography [G.P.C.] using tetrahydrofuran [THF] as the eluent.-   Mooney viscosity: Measured using an Alpha Mooney MV2000E viscometer    (Product of Alpha Technologies).-   Tensile testing: Carried out according to JIS K 6251 using an    Orientec Tensilon RTA-1T testing machine (product of Orientec Co.).-   Permanent compressive strain (Cs): Measured according to JIS K 6262.-   Hardness (Shore A peak value): Measured according to ASTM D 1415.

SYNTHESIS EXAMPLE 1

A 10-L stainless steel pressure vessel was charged with 2000 g oftetraglyme dehydrated in advance with molecular sieves and 100 g of CsFdried in advance over P₂O₅ and, after nitrogen substitution andevacuation, further charged with 200 g of CF₃CF₂COF under pressure, andmaintained at 30° C. Thereto was fed 2,2,3,3-tetrafluorooxetane underpressure in about 70-g portions at intervals of about 1 hour and thereaction was allowed to proceed. After arrival of the total charge of2,2,3,3-tetrafluorooxetane at 1750 g, the additional charging wasstopped, and the reaction was further allowed to proceed for at least 10hours. At the time when no more pressure change was observed and almostno 2,2,3,3-tetrafluorooxetane was detected in the liquid layer by gaschromatography, the residual gas was released and, after nitrogensubstitution, the autoclave was warmed to 50° C., the pressure wasreduced to about 4.0×10³ Pa to give 2470 g of CF₃CF₂CF₂OCH₂CF₂COF as acrude product.

The crude product CF₃CF₂CF₂OCH₂CF₂COF was rectified under nitrogen atordinary pressure using a 10-stage Oldershaw rectification column togive 2020 g of CF₃CF₂CF₂OCH₂CF₂COF. Its boiling point was 78° C. A 30-gportion of the CF₃CF₂CF₂OCH₂CF₂COF obtained was hydrolyzed by graduallypouring the same into 30 g of dilute sulfuric acid with stirring. Theproduct was washed several times with dilute sulfuric acid and thendistilled under reduced pressure to give 20.5 g of pureCF₃CF₂CF₂OCH₂CF₂COOH. The thus-obtained CF₃CF₂CF₂OCH₂CF₂COOH had aboiling point of 84° C. at a pressure of about 2.7×10³ Pa. A 5.9-gportion of the CF₃CF₂CF₂OCH₂CF₂COOH obtained was dissolved completely in29.8 g of pure water. The pH of the solution was 1.28. The pH wasadjusted to 7 by adding an aqueous solution of sodium hydroxidedropwise. The resulting aqueous solution contained 19.8% by mass ofCF₃CF₂CF₂OCH₂CF₂COONa. The aqueous solution was dried under vacuum at80° C., and the melting point of the CF₃CF₂CF₂OCH₂CF₂COONa obtained(solid salt) was measured by DSC and found to be 191.8° C. A 0.2% (bymass) aqueous solution of this CF₃CF₂CF₂OCH₂CF₂COONa had a surfacetension of 68.5 mN/m. The surface tension of a 2.0% (by mass) aqueoussolution thereof was 48.0 mN/m.

SYNTHESIS EXAMPLE 2

An aqueous solution of CF₃CF₂CF₂OCH₂CF₂COONH₄ (20.2% by mass) wasprepared in the same manner as in Synthesis Example 1 except that theCF₃CF₂CF₂OCH₂CF₂COOH prepared in Synthesis Example 1 was neutralized topH 7 using aqueous ammonia in lieu of the aqueous solution of sodiumhydroxide.

A 0.2% (by mass) aqueous solution of the CF₃CF₂CF₂OCH₂CF₂COONH₄ obtainedhad a surface tension of 68.4 mN/m.

SYNTHESIS EXAMPLE 3

A 300-ml stainless steel pressure vessel was charged with 70 ml oftetraglyme dehydrated in advance with molecular sieves and 1.25 g ofcesium fluoride dried in advance over P₂O₅ and, after nitrogensubstitution and evacuation, further charged with 52.4 g of CF₃CF₂CF₂COFunder pressure, and maintained at 20° C. Thereto was fed about 33.2 g of2,2,3,3-tetrafluorooxetane under pressure in about six divided portionsand the reaction was allowed to proceed. The reaction was furtherallowed to proceed for at least 2 hours. At the time when no morepressure change was observed and almost no 2,2,3,3-tetrafluorooxetanewas detected in the liquid layer by gas chromatography, the residual gaswas released, and the contents were taken out and rectified to give 32.3g of pure CF₃CF₂CF₂CF₂OCH₂CF₂COF. Its boiling point was 65.0° C. at apressure of 2.5×10⁴ Pa.

A 28-g portion of the CF₃CF₂CF₂CF₂OCH₂CF₂COF obtained was hydrolyzed bygradually pouring the same into dilute sulfuric acid with stirring. Theproduct was washed several times with dilute sulfuric acid and distilledunder reduced pressure to give 25.7 g of pure CF₃CF₂CF₂CF₂OCH₂CF₂COOH.The CF₃CF₂CF₂CF₂OCH₂CF₂COOH obtained had a boiling point of 75.5° C. ata pressure of 1.3×10³ Pa. A 3.0-g portion of the CF₃CF₂CF₂CF₂OCH₂CF₂COOHobtained was neutralized with an aqueous solution of sodium hydroxide,and the product was dried to give the desired compound. A 0.2% (by mass)aqueous solution of this CF₃CF₂CF₂CF₂OCH₂CF₂COONa had a surface tensionof 63.4 mN/m. A 2.0% (by mass) aqueous solution thereof had a surfacetension of 37.5 mN/m.

SYNTHESIS EXAMPLE 4

An aqueous solution of CF₃CF₂CF₂CF₂OCH₂CF₂COONH₄ was prepared in thesame manner as in Synthesis Example 1 except that theCF₃CF₂CF₂CF₂OCH₂CF₂COOH prepared in Synthesis Example 3 was neutralizedto pH 7 using aqueous ammonia in lieu of the aqueous solution of sodiumhydroxide.

SYNTHESIS EXAMPLE 5

A 100-ml PFA-made vessel equipped with a gas inlet pipe was charged with39.6 g of the CF₃CF₂CF₂OCH₂CF₂COOH prepared in Synthesis Example 1, andnitrogen was passed through the vessel at a flow rate of 20 ml/minutefor 10 minutes to deprive the system of oxygen and moisture. Fluorinegas diluted to 24% with nitrogen was passed through the vessel warmed ona water bath at 60° C. at a flow rate of 40 ml/minute for 15.3 hours.After substitution of the vessel inside atmosphere with nitrogen, 37.5 gof the reaction product was recovered. This reaction product wasrectified at ordinary pressure to give 25.1 g of fraction 1 (boilingpoint 58° C.) and 11.9 g of fraction 2 (boiling point 80.5° C.). Gaschromatography revealed that the fraction 1 had a purity of 95% and thefraction 2 had a purity of 99.5%. Based on the results of F-NMR, thefraction 1 was identified as CF₃CF₂CF₂OCF₂CF₂COOH in view of theappearance of a spectral peak at −123.3 ppm and the fraction 2 asCF₃CF₂CF₂OCHFCF₂COOH in view of the appearance of a spectral peak at−148.4 ppm. A 1-g portion of each fraction was dissolved in 10 g ofwater, the solution was adjusted to pH 8 by addition of aqueous ammonia,followed by drying at 80° C. under vacuum. Thus were obtainedCF₃CF₂CF₂OCF₂CF₂COONH₄ and CF₃CF₂CF₂OCHFCF₂COONH₄, respectively.

Preparation of VDF/HFP Polymer Latexes

EXAMPLE 1

CF₃CF₂CF₂OCH₂CF₂COONa (0.4 g) was dissolved in 200 mL of pure water, thesolution was placed in a 500-mL autoclave and, after nitrogensubstitution, the autoclave was charged with VDF and HFP (mole ratio:VDF:HFP=65:35) as monomers, and the monomers (mole ratio: VDF:HFP=65:35)were further fed, under pressure (0.85 MPa), to the autoclave at 80° C.An aqueous APS solution composed of 0.04 g of ammonium persulfate (APS)and 2.00 g of pure water was added to start the polymerization. Afterpressure reduction to a predetermined level of 0.75 MPa, the abovegaseous monomers (mole ratio: VDF:HFP=78:22) were fed to restore thepressure of 0.85 MPa. The procedure for feeding the above VDF and HFPwas carried out for 3 hours, the residual monomers were then removed,the autoclave was cooled, and the contents were taken out. The aqueousdispersion taken out had a solid matter content (P.C.) of 5.9% by massand the fluoropolymer had an average primary particle diameter of 102.8nm. The composition of the fluoropolymer produced was determined byF-NMR; the monomer mole ratio was VDF:HFP=78:22.

EXAMPLE 2

The polymerization of Example 1 was conducted in the same manner for 6hours except that the amount of CF₃CF₂CF₂OCH₂CF₂COONa was changed to 4g. The aqueous dispersion obtained had a solid matter content of 5.0% bymass and the fluoropolymer had an average primary particle diameter of50.7 nm. The composition of the fluoropolymer produced was determined byF-NMR; the monomer mole ratio was VDF:HFP=79:21.

EXAMPLE 3

The polymerization of Example 1 was conducted in the same manner for 3hours except that CF₃CF₂CF₂OCH₂CF₂COONH₄ was used in lieu ofCF₃CF₂CF₂OCH₂CF₂COONa. The aqueous dispersion obtained had a solidmatter content of 5.4% by mass and the fluoropolymer had an averageprimary particle diameter of 217.3 nm. The composition of thefluoropolymer produced was determined by F-NMR; the monomer mole ratiowas VDF:HFP=79:21.

EXAMPLE 4

A 3-L autoclave was used. This was charged with 1366 mL of pure waterand 2.74 g of CF₃CF₂CF₂OCH₂CF₂COONa, and the polymerization of VDF andHFP was started at a polymerization pressure of 1.55 MPa in the samemanner as in Example 1 for 18.8 hours except that, after pressurereduction to 1.45 MPa, VDF and HFP were additionally fed and, at thetime of arrival of the amount of the additional monomers at 8 g, 2.94 gof I(CF₂CF₂)₂I was fed and additional portions of ammonium persulfatewere fed at 3-hour intervals. The aqueous dispersion obtained had asolid matter content of 28.2% by mass and the fluoropolymer had anaverage primary particle diameter of 266.6 nm. The composition of thefluoropolymer produced was determined by F-NMR; the monomer mole ratiowas VDF:HFP=76:24.

Preparation of an Elastomer Comprising VDF/HFP Polymer

EXAMPLE 5

The aqueous dispersion obtained in Example 4 was coagulated usingpotassium ammonium sulfate (potassium alum), and the aggregate waswashed with pure water and dried at 130° C. for 12 hours. An elastomericVDF/HFP polymer was obtained which had a Mooney viscosity of ML₁₊₁₀(100° C.)=28.6. The composition of the fluoropolymer produced wasdetermined by F-NMR; the monomer mole ratio was VDF:HFP=76:24. A 0.1%(by mass) solution in THF was prepared from the elastomeric VDF/HFPpolymer obtained and measured for number average molecular weight,weight average molecular weight and molecular weight distribution. Noinsoluble fraction was observed. Mn=62000, Mw=89000, Mw/Mn=1.4, and onlya single peak was found.

A 100-part portion of the above solution of the VDF/HFP polymer in THF,20 parts of MT carbon, 4 parts of triallyl isocyanurate [TAIC] and 1.5parts of a dialkyl peroxide [crosslinking agent; trademark: Perhexa 25B(product of NOF Corp.)] were kneaded together on a 6-inch rubber roll.The composition obtained was subjected to cure degree testing at 160° C.using a JSR model II curastometer. The results are shown in Table 1.

TABLE 1 ML (minimum cure degree) (kg•f) 0.05 MH (maximum cure degree)(kg•f) 3.5 T10 (Induction time) 1.1 T90 (Optimum cure time) 3.3 (Note)${{T10} = \frac{{MH} - {ML}}{{10 + \left( {{Time}\mspace{14mu}{until}\mspace{14mu}{arrival}\mspace{14mu}{at}\mspace{14mu}{ML}\mspace{14mu}\left( {\min.} \right)} \right)}\;}}\;$${T90} = \frac{{MH} - {ML}}{{90 + \left( {{Time}\mspace{14mu}{until}\mspace{14mu}{arrival}\mspace{14mu}{at}\mspace{14mu}{ML}\mspace{14mu}\left( {\min.} \right)} \right)}\;}$

As shown in Table 1, the composition obtained was found to show goodcuring characteristics.

Using the above composition, 2-mm-thick sheets and P-24 O rings weremolded by press curing (primary curing; 160° C.×10 minutes), followed byoven curing (secondary curing; 180° C.×4 hours).

No. 4 dumbbell test specimens were punched out from the 2-mm-thicksheets and subjected to tensile testing.

Further, the above P-24 O rings were subjected to 25% compression underthe conditions of 200° C. for 72 hours, and the permanent compressionstrain (Cs) was measured.

Further, the hardness (Shore A peak value) was measured by the methoddescribed hereinabove.

The results are shown in Table 2.

TABLE 2 Item (unit) 100% Modulus (MPa) 2.03 Breaking strength (MPa) 21.2Elongation at break (%) 440 Hardness (Shore A peak value) 65.8 Permanentcompression strain (%) 25.85

As is shown in Table 2, the elastomeric composition obtained was foundto be high in tensile strength and low in permanent compression strain.

COMPARATIVE EXAMPLE 1

The polymerization procedure of Example 4 was carried out in the samemanner except that CF₃CF₂CF₂OCH₂CF₂COONa was not used. At the finalstage of polymerization, the rotation of the stirrer was out of order,and it became difficult to maintain the stirring during cooling aftercompletion of the polymerization. About half of the polymer formed bypolymerization was found abundantly sticking to the inside wall of theautoclave and to the stirrer shaft.

Preparation of PTFE Aqueous Dispersions

EXAMPLE 6

A 3-L stainless steel autoclave equipped with a stirring blade wascharged with 1.5 L of deionized water, 60 g of paraffin wax (meltingpoint 60° C.) and 86 mg of CF₃CF₂CF₂OCH₂CF₂COONH₄, and the system insidewas substituted with TFE. The inside temperature was raised to 70° C.,TFE was fed under pressure to an inside pressure of 0.78 MPa, and 5 g ofa 0.6% (by mass) aqueous solution of ammonium persulfate [APS] was fedto initiate the reaction. To compensate the pressure reduction in thepolymerization system with the progress of the polymerization, TFE wascontinuously fed to maintain the inside pressure at 0.78 MPa and, inthis manner, the reaction was continued. At 1.4 hours after the start ofpolymerization, TFE was purged away to terminate the polymerization. Thesolid matter concentration of the aqueous dispersion obtained was 6.5%by mass, the standard specific gravity was 2.230, and the averageprimary particle diameter of the fluoropolymer was 340 nm.

EXAMPLE 7

The reaction of Example 6 was carried out in the same manner for 5.5hours except that the amount of CF₃CF₂CF₂OCH₂CF₂COONH₄ was changed to8600 mg. The solid matter concentration of the aqueous dispersion was29.2% by mass, the standard specific gravity was 2.211, and the averageprimary particle diameter of the fluoropolymer was 365 nm.

EXAMPLE 8

The reaction of Example 6 was carried out in the same manner for 8.7hours except that 1.81 g of CF₃CF₂CF₂OCF₂CF₂COONH₄ was used in lieu ofCF₃CF₂CF₂OCH₂CF₂COONH₄. The solid matter concentration of the aqueousdispersion was 22.1% by mass, the standard specific gravity of the resinwas 2.221, and the average primary particle diameter was 274 nm.

EXAMPLE 9

The reaction of Example 6 was carried out in the same manner for 2.7hours except that 1.72 g of CF₃CF₂CF₂OCHFCF₂COONH₄ was used in lieu ofCF₃CF₂CF₂OCH₂CF₂COONH₄. The solid matter concentration of the aqueousdispersion was 13.5% by mass, the standard specific gravity of the resinwas 2.223, and the average primary particle diameter was 340 nm.

INDUSTRIAL APPLICABILITY

The fluoroalkylcarboxylic acid derivatives of the invention can beapplied, for example, as surfactants in the production of fluoropolymersand as dispersants for fluoropolymer aqueous dispersion.

1. A method of producing a fluoropolymer, wherein afluoroalkylcarboxylic acid derivative which is represented by thegeneral formula (ii):Rf¹(OCH₂CF₂CF₂)_(n1)OCHX¹CF₂(Rf²)_(n2)COOM  (ii) wherein Rf¹ representsa straight or branched fluoroalkyl group containing 1 to 20 carbonatoms, said fluoroalkyl group may optionally contain 1 to 5 oxygen atomsin the principal chain thereof, Rf² represents a straight or branchedfluoroalkylene group containing 1 to 25 carbon atoms, saidfluoroalkylene group may optionally contain 1 to 5 oxygen atoms in theprincipal chain thereof, n1 represents an integer of 0 to 3, n2represents an integer of 0 or 1, X¹ represents hydrogen atom or fluorineatom, and M represents NH₄ or a monovalent metal element, is used as asurfactant in carrying out a polymerization in an aqueous medium.
 2. Themethod of producing the fluoropolymer according to claim 1, wherein thefluoroalkylcarboxylic acid derivative is used in an amount of 0.0001 to20% by mass relative to the aqueous medium.